Lipinska Agnieszka P, Toda Nicholas R T, Heesch Svenja, Peters Akira F, Cock J Mark, Coelho Susana M
Sorbonne Université, UPMC Univ Paris 06, CNRS, Algal Genetics Group, UMR 8227, Integrative Biology of Marine Models, Station Biologique de Roscoff, CS 90074, F-29688, Roscoff, France.
Bezhin Rosko, 29250, Santec, France.
Genome Biol. 2017 Jun 8;18(1):104. doi: 10.1186/s13059-017-1201-7.
Long-term evolution of sex chromosomes is a dynamic process shaped by gene gain and gene loss. Sex chromosome gene traffic has been studied in XY and ZW systems but no detailed analyses have been carried out for haploid phase UV sex chromosomes. Here, we explore sex-specific sequences of seven brown algal species to understand the dynamics of the sex-determining region (SDR) gene content across 100 million years of evolution.
A core set of sex-linked genes is conserved across all the species investigated, but we also identify modifications of both the U and the V SDRs that occurred in a lineage-specific fashion. These modifications involve gene loss, gene gain and relocation of genes from the SDR to autosomes. Evolutionary analyses suggest that the SDR genes are evolving rapidly and that this is due to relaxed purifying selection. Expression analysis indicates that genes that were acquired from the autosomes have been retained in the SDR because they confer a sex-specific role in reproduction. By examining retroposed genes in Saccharina japonica, we demonstrate that UV sex chromosomes have generated a disproportionate number of functional orphan retrogenes compared with autosomes. Movement of genes out of the UV sex chromosome could be a means to compensate for gene loss from the non-recombining region, as has been suggested for Y-derived retrogenes in XY sexual systems.
This study provides the first analysis of gene traffic in a haploid UV system and identifies several features of general relevance to the evolution of sex chromosomes.
性染色体的长期进化是一个由基因获得和基因丢失塑造的动态过程。XY和ZW系统中的性染色体基因转移已得到研究，但对于单倍体阶段的UV性染色体尚未进行详细分析。在此，我们探究了七种褐藻物种的性别特异性序列，以了解在一亿年的进化过程中性别决定区域（SDR）基因含量的动态变化。
在所有研究的物种中，一组核心的性连锁基因是保守的，但我们也鉴定出了U和V SDRs以谱系特异性方式发生的修饰。这些修饰包括基因丢失、基因获得以及基因从SDR转移到常染色体。进化分析表明，SDR基因进化迅速，这是由于纯化选择放松所致。表达分析表明，从常染色体获得的基因已保留在SDR中，因为它们在繁殖中具有性别特异性作用。通过检查海带中的逆转座基因，我们证明与常染色体相比，UV性染色体产生了数量不成比例的功能性孤儿逆转录基因。基因从UV性染色体中移出可能是一种补偿非重组区域基因丢失的方式，正如XY性系统中Y衍生的逆转录基因所表明的那样。
本研究首次分析了单倍体UV系统中的基因转移，并确定了与性染色体进化普遍相关的几个特征。
